Antibody drug conjugates (ADC) are targeted chemotherapeutic molecules combining the properties of both antibodies and cytotoxic drugs by targeting potent cytotoxic drugs to antigen-expressing tumor cells, internalization, and release of drug, thereby enhancing their anti-tumor activity (Carter, P. and Senter, P. (2008) The Cancer Jour. 14(3):154-169). Successful ADC development for a given target antigen depends on optimization of antibody selection, linker design and stability, cytotoxic drug potency and mode of drug and linker conjugation to the antibody (Polakis, P. (2005) Current Opinion in Pharmacology 5:382-387).
KADCYLA® (trastuzumab emtansine, Genentech) has recently been approved for the treatment of breast cancer. Trastuzumab emtansine is an antibody-drug conjugate with a maytansine drug moiety DM1 covalently attached via a stable, non-disulfide linker MCC to the anti-HER2 antibody trastuzumab (Phillips G. et al. (2008) Cancer Res. 68:9280-90). Trastuzumab is the antibody formulated as HERCEPTIN® (Genentech), approved in 1998 for HER2 positive breast cancer therapy.
Anthracyclines are used in the treatment of numerous cancers such as leukemia, breast carcinoma, lung carcinoma, ovarian adenocarcinoma and sarcomas. Commonly used anthracyclines include doxorubicin, epirubicin, idarubicin and daunomycin. Morpholino analogs of doxorubicin and daunorubicin, formed by cyclization on the glycoside amino group, have greater potency (Acton et al (1984) J. Med. Chem. 638-645; U.S. Pat. No. 4,464,529; U.S. Pat. No. 4,672,057; U.S. Pat. No. 5,304,687). Nemorubicin is a semisynthetic analog of doxorubicin with a 2-methoxymorpholino group on the glycoside amino of doxorubicin and has been under clinical evaluation (Grandi et al (1990) Cancer Treat. Rew. 17:133; Ripamonti et al (1992) Brit. J. Cancer 65:703), including phase II/III trials for hepatocellular carcinoma (Sun et al (2003) Proceedings of the American Society for Clinical Oncology 22, Abs1448; Quintieri (2003) Proceedings of the American Association of Cancer Research, 44:1st Ed, Abs 4649; Pacciarini et al (2006) Jour. Clin. Oncology 24:14116). Immunoconjugates and prodrugs of daunorubicin and doxorubicin have been prepared and studied (Kratz et al (2006) Current Med. Chem. 13:477-523; Jeffrey et al (2006) Bioorganic & Med. Chem. Letters 16:358-362; Torgov et al (2005) Bioconj. Chem. 16:717-721; Nagy et al (2000) Proc. Natl. Acad. Sci. 97:829-834; Dubowchik et al (2002) Bioorg. & Med. Chem. Letters 12:1529-1532; King et al (2002) J. Med. Chem. 45:4336-4343; U.S. Pat. No. 6,630,579). The antibody-drug conjugate BR96-doxorubicin reacts specifically with the tumor-associated antigen Lewis-Y and has been evaluated in phase I and II studies (Saleh et al (2000) J. Clin. Oncology 18:2282-2292; Ajani et al (2000) Cancer Jour. 6:78-81; Tolcher et al (1999) J. Clin. Oncology 17:478-484).
Several metabolites of nemorubicin (MMDX) from liver microsomes have been characterized, including PNU-159682, (Quintieri et al (2005) Clinical Cancer Research, 11(4):1608-1617; Beulz-Riche et al (2001) Fundamental & Clinical Pharmacology, 15(6):373-378; EP 0889898; WO 2004/082689; WO 2004/082579). PNU-159682 was remarkably more cytotoxic than nemorubicin and doxorubicin in vitro, and was effective in vivo tumor models. PNU-159682 is named as 3′-deamino-3″,4′-anhydro-[2″(S)-methoxy-3″(R)-oxy-4″-morpholinyl]doxorubicin, and has the structure:

Certain PNU-159682 antibody-drug conjugates have been described (WO 2009/099741; WO 2010/009124; U.S. Pat. No. 8,742,076; U.S. Pat. No. 8,389,697). Processes for making PNU-159682 analogs are described (U.S. Pat. No. 8,470,984).